In magnetic induction betatron accelerators ("betatrons"), electrons are accelerated by an electric field induced by a changing magnetic flux linking the orbit of electrons in a circular path around the magnetic flux. The energy gained by an electron in one revolution about the flux is equivalent to the induced voltage in a one-turn coil having the electron orbit dimensions. Since electron velocities are large, approaching the speed of light at a few Mev, the electrons make many revolutions in a short time and acquire a high energy.
The general theory of betatrons is well known. See, e.g., M. Stanley Livingston et al., "The Betatron--Magnetic Induction Accelerator," Particle Accelerators, McGraw-Hill Book Company (1962); U.S. Pat. No. 2,697,167, "Induction Accelerator," issued Dec. 14, 1954, to Kerst; U.S. Pat. No. 4,577,156, "Push-Pull Betatron Pair," issued Mar. 18, 1986, to Kerst. All of these references are incorporated herein by reference.
Acceleration of the electrons is obtained from the changing magnetic field in a magnetic core about which the electron orbits. An increasing flux field provides the electric field necessary for electron acceleration. However, the maximum magnetic field change that can be obtained is the difference between a minimum field and a maximum field, generally defined by a sinusoidal wave shape. The energetic electrons must be removed before the magnetic flux begins to decrease and a decelerating electrical field is produced. All known prior betatrons have been constrained by this flux swing limitation, where the maximum energy gain can be shown to be EQU .DELTA.E.ltoreq.E.sub.max (MeV).apprxeq.300R.sub.c B.sub.s,(1)
where E is the electron energy, B.sub.s is the core saturation flux field in Tesla and R.sub.c is the radius of the magnetic core in meters.
It is seen from the above equation that any electron energy increase is generally proportional to R.sub.c, since B.sub.s is an intrinsic property of the material selected for the magnetic core. However, the mass of the magnet system (core plus return yoke) is a function of R.sub.c.sup.3, and this mass becomes prohibitively large for high energy betatrons.
This and other problems of the prior art are addressed by the present invention wherein two betatrons are provided in tandem to enable multiple flux swings to be used to accelerate electrons to high energies. Accordingly, it is an object of the present invention to eliminate the flux swing limitation on electron acceleration in magnetic induction accelerators.
Another object of the present invention is to provide betatrons having reduced magnetic core mass with an equal energy output as conventional betatrons.
One other object of the present invention is to remove electron energy output from being proportional to the radius of the betatron core in order to minimize the magnet mass needed for a given electron energy output.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.